Simplify the following expression: $y = \dfrac{x}{10} + \dfrac{x}{8}$
Explanation: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $10$ and $8$ $\lcm(10, 8) = 40$ $ y = \dfrac{4}{4} \cdot \dfrac{x}{10} + \dfrac{5}{5} \cdot \dfrac{x}{8} $ $y = \dfrac{4x}{40} + \dfrac{5x}{40}$ $y = \dfrac{4x +5x}{40}$ $y = \dfrac{9x}{40}$